Capacitors are used extensively in electronic devices for storing an electric charge. Capacitors essentially comprise two conductive plates separated by an insulator. Capacitors are used in filters, analog-to-digital converters, memory devices, various control applications, and mixed signal and analog devices, for example.
There is a demand in semiconductor device technology to integrate many different functions on a single chip, e.g. manufacturing analog and digital circuitry on the same die. MIM capacitor (MIMcap's) are often used in these integrated circuits. A MIM capacitor is a particular type of capacitor having two metal plates sandwiched around a capacitor dielectric that is parallel to a semiconductor wafer surface. They are rather large in size, being several hundred micrometers wide, for example, depending on the capacitance, which is much larger than a transistor or memory cell, for example. MIM capacitors are typically used as decoupling capacitors for microprocessor units (MPU's), RF capacitors in high frequency circuits, and filter and analog capacitors in mixed-signal products, as examples.
To form a MIM capacitor, the top capacitor metal plate is formed by a planar deposition of a conductive material, and lithographically patterning and etching the conductive material using a reactive ion etch (RIE) process, for example. The patterning of the top metal plate requires the use of a mask, and there can be alignment problems to underlying features (e.g., the MIM capacitor bottom plate) and vias to connect to interconnect layers.
Another problem in fabricating MIM capacitors is a restriction in the selection of the MIM dielectric materials, due to potential interaction with or diffusion of the metals (such as copper) used for the metal plates. The MIM dielectric material restriction may result in limited area capacitance.
Another problem in fabricating MIM capacitors is that, in order to avoid problems that arise in fabricating semiconductor devices using copper, often higher resistive plate materials such as aluminum, titanium nitride, and tungsten, as examples, are used for the top and bottom metal plates, which results in reduced high frequency capability. The use of copper, which has a lower resistivity, for the top and bottom metal plates is therefore desired. The use of copper for the top and bottom metal capacitor plates also produces a MIM capacitor having higher quality factors (Q-values).
A further problem in the manufacturing of MIM capacitors is etch stop problems during subsequent via etches. Vias are typically used to connect the top and bottom metal plates to subsequently formed metallization layers. Because of topography differences for the top and bottom metal plates, more insulating material must be etched to reach the bottom plate than to reach the top plate, and this can create etch stop problems when etching the vias.
What is needed in the art is an improved integration scheme for fabricating a MIM capacitor that solves these problems in the prior art.